The magnetic encoder device used to detect the rotating speed (number of rotations) of a rotating body has a variety of number of applications and is composed of: a magnetic encoder including an annular support member for attachment to the rotating body and an annular magnet member that is fixed to the support member and has N and S poles magnetized circumferentially at regular intervals in a multipolar manner; and a sensor that is attached to a non-rotating body so as to be opposed to the magnet member for detecting rotation of the magnet member.
As the magnet member of the magnetic encoder, a rubber magnet is widely used but also a plastic magnet is used for the purpose of improvement in detection accuracy with increase of magnet force and the like. Specifically, an annular plastic magnet is injection-molded, a thermoset adhesive is applied to an adhesion surface of the annular plastic magnet, and the annular plastic magnet is adhered to a support member to form a magnetic encoder (for example, refer to Patent Document 1), or an annular plastic magnet is injection-molded with a support member as an insert while a thermoset adhesive is applied to a joint surface of the insert with respect to the plastic magnet, thereby to form a magnetic encoder having a wrap-around portion at the outer peripheral side (for example, refer to Patent Document 2), or an annular plastic magnet is injection-molded with, as an insert, a support member having a large number of radiation grooves opened in an inner-diameter direction in a joint surface with respect to an annular plastic magnet while no thermoset adhesive is applied to the joint surface, thereby to form a magnetic encoder having a wrap-around portion at the inner peripheral side (for example, refer to Patent Document 3).